Exploding bridgewire device



Oct. 11, 1966 w. s. BANKSTON EXPLODING BRIDGEWIRE DEVICE Filed July 15, 1964 United States Patent 3,277,824 EXPLODENG BRIDGEWIRE DEVICE Weldon S. Bankston, Miraleste, Calif., assignor to Hi- Shear Corporation, Torrance, Calif., a corporation of California Filed July 15, 1964, Ser. No. 382,811 8 Claims. (Cl. 102-28) This invention relates to the detonation of explosive charges.

There are many applications wherein gas-forming materials are detonated in order to provide power for actuating a device such as a separable nut, or for initiating the detonation of still a larger charge, or for carrying out [mechanical operations by the release of power. Often these devices are called detonators. Frequently they utilize the passage of a current through a portion of the charge to detonate the charge or a primer.

There are a number of considerations which have to be kept in mind when designing devices of this type, and one of the primary ones is that of sensitivity of the material to mechanical shock and to stray electric currents. For example, a material which can readily be detonated is likely to be dangerous in the event that the detonator carrying it is dropped on the floor. It is a good thing to prevent such an occurrence by not dropping the device at all, but an even safer approach is to use relatively less sensitive material. However, as materials are made less sensitive, they are also rendered more difilcult to detonate. Another problem in the use of devices which include bridgewires and gaps is that in many environments there are stray static electric charges which might be discharged through the are or bridgewire, thereby accidentally detonating the device. Again, a Way to protect against this is to use a less sensitive charge.

It is an object of this invention to provide an explosive device which is able to utilize material which is more insensitive to mechanical shock and to the effects of stray electric charges than materials which are useful in presently-known devices.

It is another object of this invention to provide a detonator-type device which can serve as a switch to control heavy currents in associated equipment, in one-shot use.

A device according to this invention includes in combination a body which mounts a first pair of spaced-apart electrodes that fiorm a gap adapted to be bridged by an electrical discharge. A second pair of spaced-apart electrodes is mounted to the body, and an explodable, vaporizable conductive bridgewire interconnects the second pair of electrodes. The bridgewire is so disposed and arranged as to apply, when exploded, a bridge of plasma between the first pair of electrodes, thereby to complete a circuit for passage of an electrical discharge between them.

According to a preferred but optional feature of this invention, both pairs of electrodes are connected across respective capacitors, the explosion of the bridgewire being triggered by discharge of its respective capacitor therethrough. The discharge produces a peak wave which explodes the bridgewire in accordance with known principles.

According to still another preferred but optional feature of this invention, the device is utilized in combination with a load which itself is connected to a source of energy, the first pair of electrodes being connected in series therewith as a break in the load circuit, whereby the plasma bridge derived from the explosion of the bridgewire completes the load circuit and permits the load to be energized.

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The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings in which:

FIG. 1 is a side elevation, partly in cutaway crosssection of one embodiment of the invention;

FIG. 2 is a fragmentary cross-section of the invention taken at line 22 of FIG. 1;

FIG. 3 is a circuit diagram showing the use of the device of FIG. 1;

FIG. 4 is a fragmentary cross-section showing another embodiment of the invention;

FIG. 5 shows a circuit utilizing the device of FIGS. 1 or 4 to trigger still another circuit;

FIG. 6 is a cross-section of another embodiment of the invention taken at line 6--6 of FIG. 7;

FIG. 7 is a cross-section taken at line 77 of FIG. 6;

FIG. 8 is a cross-section of the presently preferred embodiment of the invention taken at line 88 of FIG. 9; and

FIGS. 9 and 10 are top and bottom views of FIG. 8 taken at lines 9-9 and 10-10, respectively, therein.

One embodiment of detonator 10 according to this invention is shown in FIG. 1. It includes a case 11 with a longitudinal axis 12, and a top 13. Top 13 has a reduced central region 14. A body 15 is fitted inside the base, the body being of non-conductive, insulating material. In order to focus certain shock waves yet to be described, a trough 16 comprising a pair of surfaces 17, 18 forming a dihedral angle, is formed in the top of the body. A bridgewire 19 lies in the bottom of the trough, along the dihedral edge. The bridgewire is a type which produces, when exploded by a current of the proper wave-form, optimum shock waves.

A first pair of spaced-apart electrodes 20, 21 passes through the body to form prongs 22, 23 which can be plugged into, or otherwise conductively connected to, an electrical system. Discharge points 24, 25 extend into the trough through surfaces 17, 18, respectively, to form a gap 26 adapted to be bridged by an electrical discharge. This gap lies at to the bridgewire below it. A second pair of spaced-apart electrodes 27, 28 also passes through the body and extends beyond the case to form prongs 29, 30, respectively. Electrodes 27 and 28 are conductively connected to opposite ends of the bridgewire.

Above the body and inside the case, there is formed a chamber 31 which is filled with an explosive material 32. The term explosive material as used herein means a solid material which can be detonated, thereby to convert itself to gaseous products at relatively high temperature and pressure. Suitable examples of materials for use in this invention are RDX and PETN, which are wellknown, relatively insensitive explosives. The explosive material is packed into the chamber so as to surround and to be in contact with the bridgewire and with the first pair of electrodes filling the space between them.

A first capacitor 35 (FIG. 3) has a first and a second terminal 36, 37, respectively. An off-on switch 38, which may be a triggering circuit, if desired, has a first terminal 39 and a second terminal 40, respectively. The second terminals are connected to each other, and first terminals 36 and 39 are respectively connected to prongs 29 and 30 of electrodes 27 and 28. A second capacitor 41 is connected to prongs 22 and 23, thereby being connected across electrodes 20 and 21. As examples, capacitor 35 may conveniently have a rating of 2000 volts, 1 microfarad. A similar rating is provided for second capacitor 41, although it may be somewhat less, if desired. Bridgewire 19 is preferably gold wire about 2 /2 mils, long. It is preferably spaced about A3" to A" below gap 26.

FIG. 4 illustrates an optional embodiment of body 45 suitable for use with this invention, it having the same 3 electrodes and materials of construction in the device of FIG. 1. The difference is that top surface 46 of body 47 is fiat, and the bridgewire lays against this surface. This bridgewire is below the gap, as is the case in FIG. 2, the difference being that no effort is made to focus the shock waves at the gap in this device.

FIG. 5 shows detonator in simplified notation and the same notations are used, except that the circuitry of the first pair of electrodes is brought through the sides for simplicity in disclosure. The purpose of circuit 50 shown therein is to provide a one-shot control over the discharge of a heavy current such as 50,000 amperes through a load 51. The charge applied to load 51 may be stored on a third capacitor 52. The capacitor is connected in series with load 51 and with electrodes 20, 21 of detonator 10.

FIG. 6 illustrates how second capacitor 41 may, if desired, be carried directly by body 15. This capacitor is a Wound Mylar foil type wherein two strips of Mylar or other dielectric material 55, 56 are sandwiched with two layers of foil 57, 58. This sandwich is wound around the body, and prongs 22, 23 may be connected directly to the two metal layers as shown in FIG. '7. This is a common capacitor construction.

The presently preferred embodiment of the invention is shown in FIGS. 8-10. It includes a body 70 of the same material as body 15, and is adapted to fit inside the same case as the device of FIG. 1. The significant differences reside in the top surface of the body. Instead of a groove, it is provided with a concave conical surface 71.

A first pair of spaced-apart electrodes 72, 73 passes through the body and terminates at the conical surface, where the ends of the electrodes may or may not be extended into the conical region. As shown, they simply terminate flush with the surface.

A bridgewire having two arms 74, 75, connects to three electrodes 76, 77, 78, which pass through the body. The

bridgewire arms rest upon the conical surface. Electrode 77 is one circuit terminal, and electrodes 76 and 78 form another circuit terminal. They may either be connected together inside the body, or run out through separate prongs and connected by circuitry outside the body, as preferred.

Prongs 79, 80, 81, 82 and 83, are connected to, and respective to, electrodes 72, 73, 76, 77 and 78. One of electrodes 81 and 83 may be eliminated if electrodes 76 and 78 are connected together in the device. Two bridgewire circuits in parallel are formed in this device. Both depart from electrode 77, and branch respectively to electrodes 76 and 78. The bridgewire arms lite at 90 to the gap between electrodes 72 and 73.

The explosive material will be packed against and above the conical surface, as it is packed against and above the groove in FIG. 1.

The operation of this device will now be described. With detonator 10 connected into a circuit such as that of FIG. 3, capacitors 35 and 41 are charged by any desired charging circuit. In the device shown, both capacitors are charged to 2000 volts. It is of importance to note that in the example given, the material is so insensitive to electrical discharge that even accidental discharge of capacitor 41 through the material will not detonate it. It is possible, of course, to utilize material which is more sensitive to a spark, but this would give up some of the advantages of the invention. The principal advantage of the invention as shown is that it takes more to detonate the material. A combination of shock and heat waves from the explosion of the bridgewire will apply a plasma bridge to gap 26, thereby to trigger the discharge of the second capacitor through said gap, and release its energy as heat, all of which occurs substantially instantaneously so that there is at the gap for a very brief moment a combination of shock and heat waves from the explosion of the bridgewire and also of heat from the discharge of the second capacitor. This is a bootstrap effect, and applies a very W current loads.

4- great and sudden pulse of two types of energy to the insensitive material, and is enough to set it off. This is in fact a high voltage device, but the voltages are able to be handled with great safety.

In FIGS. 1 and 8, the concave regions focus the heat and shock waves from the exploding bridgewire to the gap. However, many times this feature will be found unnecessary, and the simpler construction of FIG. 4 can be used instead.

In FIG. 5, the explosion of the bridgewire occasioned by closing switch 38 provides a bridge of plasma across gap 26, thereby closing the circuit through load 51. This may be a current of any desired level such as perhaps 50,000 amperes. It will be observed that this is a very simple and inexpensive expedient for triggering such large Presently available gas-filled tubes for this purpose are unable to handle much above 1000 amps, and cost many times the amount of this simple, single-shot device.

FIGS. 6 and 7 illustrate that second capacitor may be made integral with the body instead of being provided as a separate item. This enables a self-contained detonator to be plugged directly into a self-contained firing circuit, including the first capacitor and the switch, the firing circuit being able to be left in place and not destroyed, while the second capacitor may be destroyed, if desired, it being quite inexpensive.

Providing the bridgewire in the form of two arms opposed to each other inside a conical region (preferably between about a 60-90 included conical angle) results in a vector addition of shock waves which increases the efficiency of the device, and for this reason the device of FIG. 8 is preferred.

This invention is not to be limited by the embodiments shown in the drawings and described in the description which are given by way of example and not of limitaton, but only in accordance with the scope of the appended claims.

What is claimed is:

1. An explosive assembly comprising: a body; a first pair of spaced-apart electrodes mounted to the body and forming a gap inside the body adapted to be bridged by an electrical discharge; a second pair of spaced-apart electrodes mounted to the body; a vaporizable, conductive bridgewire interconnecting the second pair of electrodes inside the body, the gap and the bridgewire being spaced apart from each other, the bridgewire being so disposed and arranged as to apply, when exploded, a bridge of plasma between the first pair of electrodes to complete a circuit for passage of the electrical discharge therebetween; and a substance imbedding the first electrodes, the detonation of which substance is initiable by energy derived from an electrical discharge between the first electrodes which is in turn initiated by the vaporizing of the bridgewire.

2. An explosive assembly according to claim 1 in which the bridge is disposed in a concave region beneath the gap, the shape of the boundary of the region focusing energy from the vaporized bridgewire at the gap.

3. An explosive assembly according to claim 2 in which the concave region is conical and has an apex, and in which the bridgewire has a pair of opposed arms extending from a terminal at said apex.

'4. An explosion assembly according to claim 1 in which the region surrounding the bridgewire and gap is enclosed by a rupturable shell.

5. An explosive assembly according to claim 1 in which a first capacitor having a first and a second terminal, and switch means having a first and a second terminal are provided, the first terminals being conductively connected to respective electrodes of the second pair, and the second terminals being conductively connected to each other, whereby closure of the switch means enables a charge on the capacitor to flow through and vaporize the bridgewire.

5 6 6. An explosive assembly according to claim 5 in which 2,963,970 12/ 1960 Schaadt et a] 102 28 the first capacitor is integral with the body. 3,052,185 9/ 1962 Apstein 102-70.2 X 7. A11 explosive assembly according to claim 5 in which 3,070,013 12/ 196 2 Backstein et a1 102-28 a second capacitor is connected between the electrodes of 3,082,691 3/1963 Evans et 1. 1 2 2g the first pair whereby to be discharged when plasma from 5 3 15 098 11 /1964. Reithel X the vaporized bridgewire bridges said gap. 3,166,689 1/1965 .Buntenbach X 8. An explosive assembly according to claim 1 in which 3,167,014 1/1965 Kopito X the electrodes form a rectangular pattern.

R ef e r e n c e s Cited by the Examiner 10 BENJAMLN A. BO-RCHELT, Primary Examiner.

UNITED STATES PATENTS R. V. LOTTMANN, V. R. PEN'DEGRASS, 22, 3 6/19 7 Rolland 102*28 X Assistant Examiners. 

1. AN EXPLOSIVE ASSEMBLY COMPRISING: A BODY; A FIRST PAIR OF SPACED-APART ELECTRODES MOUNTED TO THE BODY AND FORMING A GAP INSIDE THE BODY ADAPTED TO BE BRIDGED BY AN ELECTRICAL DISCHARGE; A SECOND PAIR OF SPACED-APART ELECTRODES MOUNTED TO THE BODY; A VAPORIZABLE, CONDUCTIVE BRIDGEWIRE INTERCONNECTING THE SECOND PAIR OF ELECTRODES INSIDE THE BODY, THE GAP AND THE BRIDGEWIRE BEING SPACED APART FROM EACH OTHER, THE BRIDGEWIRE BEING SO DISPOSED AND ARRANGED AS TO APPLY, WHEN EXPLODED, A BRIDGE OF PLASMA BETWEEN THE FIRST PAIR OF ELECTRODES TO COMPLETE A CIRCUIT FOR PASSAGE OF THE ELECTRICAL DISCHARGE THEREBETWEEN; AND A SUBSTANCE IMDEDDING THE FIRST ELECTRODES, THE DETONATION OF WHICH SUBSTANCE IS INTIABLE BY ENERGY DERIVED FROM AN ELECTRICAL DISCHARGE BETWEEN THE FIRST ELECTRODES WHICH IS IN TURN INITIATED BY THE VAPORIZING OF THE BRIDGEWIRE. 